Well AF will be slower with the adapter and 4/3 lens, But optically they will have similar with about the same size image circles. M4/3 just have a different flange that allows it to mount different adapter. And with the 4/3 adapters. It gives the needed distance that the 4/3 lens needs to project the proper image circle on the sensor.

which shows a comparison of lens distances and diameters for the lens.

The figure gives the impression that the four thirds lens would collect light from a larger diameter and funnel it down to the sensor. Since the micro four thirds lens is closer to the sensor, it is a smaller diameter. I am not sure about the optics but initial reaction is that the four thirds would collect more light for the same sensor size compared to the micro four thirds.

I was not worried about focus times or sizes at this point, just the low light capabilities of the lens.

Without the adapter, you might be right ... but then nothing would be in focus either... in the end, the light is passing through a "hole" the same size and making an image circle the same size, so the light density must be the same.

That said, you have a whole lot more "bright" lens options in 4/3 than m4/3.

eh?..... focal length and aperture remain the same regardless of whatever size of sensor.

a 4/3 and a micro 4/3 lens of the same focal length and aperture will produce the same result.

Click to expand...

Exactly, since the sensors are the same size ... Remember that a f/1.8 aperture is a f/1.8 aperture (the adapter notwithstanding). The focal length is of no consequence in light collection, as in; a 50mm f/1.8 will collect the same amount of light as an 85mm f/1.8; a 28mm f/1.8 will collect the same amount of light as an 85mm f/1.8; et cetera.

Aperture (lens speed) is a ratio of front element diameter to distance from front element to film/sensor plane (the little symbol of a circle with a line through it on top the camera). In actuality your Nikkor 50mm is 1:1.4.

So lets say you have a f/2 50mm. It would take two front elements (diameters) to span the distance from the front of the lens to the sensor.

Remember that the light needs to be focus evenly across the entire film/sensor. Legacy glass is designed for full frame, 35mm film. So the light must be evenly spread across all four corners of that 35mm frame ... or as you stated the light must be evenly spread in a "per unit area" manner. In other words, the light hitting the center of the frame must be equal to f/1.4 and the light hitting the corners must be equal to f/1.4. (Anything else than that results in vignetting/darken corners.)

That FF glass, which spreads light evenly across a FF frame will easily spread light across a smaller surface (ala APS-C or M4/3).

The problem comes when one uses a lens designed for an APS-C sensor or a M4/3rds sensor on a FF camera. An APS-C sensor is roughly 50% smaller than a FF, so strapping on a lens designed for an APS-C sensor onto a FF camera will result in an image with significant light drop-off in the corners. A M4/3 sensor is a quarter of the size of a FF sensor and all you'll get is a circular keyhole looking image.

Aperture (lens speed) is a ratio of front element diameter to distance from front element to film/sensor plane (the little symbol of a circle with a line through it on top the camera). In actuality your Nikkor 50mm is 1:1.4.

Hope I haven't confused you more ...
Gary

Click to expand...

Um, yes you have - because your initial statement could not be more incorrect

F/stop is defined as the ratio of entrance pupil to focal length, but since entrance pupil is a calculated figure, (it is not the size of the entry lens!) the equation simplifies to focal length divided by aperture diameter. Since a longer focal length has a smaller field of view, the larger aperture diameter results in the same light density (illumination per unit area)

" F/stop is defined as the ratio of entrance pupil to focal length, but since entrance pupil is a calculated figure, (it is not the size of the entry lens!) the equation simplifies to focal length divided by aperture diameter."

I think this led to some of my confusion. I had assumed that the 4/3 lens would need a longer focal length since they are farther from the sensor. With a longer focal length, I assumed they would have a larger relative "pupil" area.

Um, yes you have - because your initial statement could not be more incorrect

F/stop is defined as the ratio of entrance pupil to focal length, but since entrance pupil is a calculated figure, (it is not the size of the entry lens!) the equation simplifies to focal length divided by aperture diameter. Since a longer focal length has a smaller field of view, the larger aperture diameter results in the same light density (illumination per unit area)

My initial statement made reference to "Lens Speed" not "F/stop", as such I believe it is accurate for this thread. I attempted to simplify the explanation and in doing so I guess I didn't didn't use the precise and confusing terminology which you insist. All-in-all to say my answer "could not be more incorrect" just isn't true, additionally, I believe my answer, in spite of its lack of precise terminology, is much easier to understand and grasp in the context of this thread. In final review of your response, you just pretty much rewrote my original statement.

This brings up my desire for someone to make a "condenser" adapter or the reverse of a teleconverter for 35mm aka FF lens for 4/3rds and APS sized sensors. Besides making them brighter it would make them the correct focal length.

No, your statement made no relation to the aperture opening of the lens - only to the physical size of the elements. In your explanation, the 45-200 with it's larger diameter primary element would be "faster" than the PL45 with it's tiny element, which we know is absolutely untrue. Look at how tiny the entry glass is on the super bright 20/1.7!

You are confusing the term "pupil" as it is used in optics - it's not a lens diameter - it is the aperture diameter after magnification. It is a relation of how much light comes through the device. It is used throughout all optics applications. For example, one of the ratings for the brightness of a rifle scope is called the exit pupil which is the objective diameter divided by the magnification, however, it is practically useless because it doesn't include the number of elements nor the coatings on the elements. For example, a well coated, expensive scope with a lower exit pupil will be MUCH brighter than a large exit pupil scope that uses uncoated optics.

To the question asked by the OP, we're getting a bit far of field. The size of the elements in the lens and the length of the lens makes no difference in the brightness of the lens.

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